2 week old Lowryder AK47 in aero/bubble system growing slowly?

hi everyone, this is my first post and my first grow, i made a diy bubble/aero system and everything seems to be working they just seem to be a little slow compared to other i have seen.

they are on 18/6 light
one is under 90w led the other under 150whps (the led one is doing a lot better)
the res temps is at 69
temp is mid 80's while lights are on but go down as low as 55 while they are off.
humidity is low 40% tops
i am using ferro nutes but a very small amount, they recommend 30ml per 10L of water im using 5ml per 10L of water as they are still small.
and the ph is between 5.5 and 6

one is doing better than the other and one has some small brow spots on one of the leaves?

if anyone has any suggestions for me i would appreciate it. i might just be worrying for no reason. they do seem to be small tho.

I have trouble with 1 out of my 6. But I'm getting the rust and can't find any info on it but wheat gets that I'm ready to try a bleach solution for root rot cure if u havnt found nothing out on the spots

Bump could really use some help. thanks